Antibacklash screw-thread adjustable rotor for low-loss capacitor

ABSTRACT

A low-loss capacitor having hollow cylindrical electrodes which are coaxially interleaved. The capacitance is varied by rotation of the rotor electrodes which are mounted on a screw member for axial displacement with respect to the stator electrodes when the screw member is turned. The screw member has a frictional-locking means in the form of a pair of diametrically opposed, outwardly bulging, thin-walled sections interspaced by through openings. A square opening is provided within the outer end of the screw member to permit adjustment thereof for tuning by use of a nonmetallic tuning rod tool of complemental square crosssectional shape.

United States Patent inventor Appl. No.

Filed Patented Assignee John E. Johanson Boonton, NJ.

Dec. 9, 1970 Nov. 30, 1971 Johanson Manufacturing Corporation Boonton,NJ.

ANTlBACKLASl-l SCREW-THREAD ADJUSTABLE ROTOR FOR LOW-LOSS CAPACITOR [56]References Cited UNITED STATES PATENTS 3,512,059 5/1970 Johanson 3l7/25lX Primary Examiner-E. A. Goldberg AllorneyJames J. Cannon ABSTRACT: Alow-loss capacitor having hollow cylindrical electrodes which arecoaxially interleaved. The capacitance is varied by rotation of therotor electrodes which are mounted on a screw member for axialdisplacement with respect to the stator electrodes when the screw memberis turned. The screw member has a frictional-locking means in the formof a pair of diametrically opposed, outwardly bulging, thin-walledsections interspaced by through openings. A square opening is providedwithin the outer end of the screw member to permit adjustment thereoffor tuning by use of a nonmetallic tuning rod tool of complementalsquare cross-sectional shape.

ANTIBACKLASII SCREW-THREAD ADJUSTABLE ROTOR FOR LOW-LOSS CAPACITOR Thisinvention relates to adjustable capacitors and is directed particularlyto improvements in friction lock adjustment screw mechanism for therotors of such capacitors.

Applicants US. Pat. No. 3,5l2,059, issued May 12, I970, describes arotatively adjustable low-loss capacitor having frictionally lockedantibacklash adjustment screw mechanism. This invention is directed toimprovements in such friction lock antibacklash capacitor adjustermechanisms.

The principal object of this invention is to provide an improvedfriction lock antibacklash tuning adjustment mechanism for rotativelyadjustable low-loss capacitors such as are used for tuning or astrimmers and which have maximum capacitances of the order of from to 500microfarads.

My invention is particularly well suited to use with electricalcapacitors comprising a stator unit and a rotar unit each having aseries of coaxially arranged, interspaced cylindrical electrode tubes.In such capacitors, the stator unit is rigidly connected by a hollowcylindrical insulating member with an interiorly threaded rotor bushing.The rotor unit comprises a rotor screw which engages the internalthreads of the rotor bushing with a precision fit. One end of the rotorscrew carries an axially displaceable group of rotor tubes which enterbetween and are spaced from the stator tubes. The outer end of the rotorscrew is formed with interengagement means for adjustably turning therotor unit with respect to the stator unit in tuning the capacitor. Insuch low-loss capacitors it is essential that the change in capacitancedrift, whether due to change in ambient temperature or other causes, bekept to an absolute minimum. Because of its cylindrical structure suchcapacitors inherently have a low-temperature capacitance coefficient. Itis, accordingly, another object of this invention to provide improvedfriction lock mechanism which will be antibacklash in nature and firm inits gripping action so as to minimize the possibility of capacitancedrift, variation or change due to mechanical displacement of the rotor,once tuned, with respect to the stator, whether caused by vibration,shock forces, or changes in temperature.

A more particular object of the invention is to provide an antibacklashscrew thread adjustable rotor for low-loss capacitors of the abovenature wherein the rotor unit comprises a substantially tubular outerend portion the outer wall of which is formed with a pair of axiallyspaced screw thread sections interjoined by a relatively thin-walledtubular section which is resiliently deformable as radially outwardlyextending bulges permitting helical misalignment of the two threadedportions upon insertion of the thus threaded rotor into the rotorbushing. The two threaded portions are thus yieldingly forced intohelical alignment by an accompanying elongation of the outwardly bulgingthin-walled intermediate portion to produce frictional engagementbetween the continuous internal threads of the rotor bushing and theinterrupted external threads of the rotor screw. The thin-walled tubularsection between the two screw thread sections is cut away atdiametrically opposed portions thereof. The thickness of theinterjoining thin-walled tubular section of the rotor unit and theperipheral extent of the diametrically opposed portions cut away isvaried in accordance with the diameter of the rotor. The invention isparticularly well suited to the manufacture of capacitors having smallerdiameter rotor member units, usually those of lower capacitance values.

Still another object of the invention is to provide an antibacklashscrew thread adjustable rotor for low-loss capacities where a squareslot is provided at the outer end of the tunable rotor, such as can beformed by a swedging operation with special tooling, to permit use of asquare-shaped rod tool of insulating material as a capacitance-adjustingdevice instead of the usual screwdriver. The use of a nonelectricallyconductive material as a tuning tool is of particular importance inhigher frequency applications. At the same time, making the rotoradjustment slot of square cross section provides for the greatest torquestrength with the simplest fabrication. Another advantage of the squarerecess-adjustment slot comprising the invention is that it eliminatesscraping of the internal threads of the rotor bushing caused by thestandard metal screwdriver used in transversely slotted capacitor rotorsheretofore known.

Other objects, features and advantages of the invention will be apparentfrom the following description when read with reference to theaccompanying drawings. In the drawings, wherein like reference numeralsdenote corresponding parts throughout the several views:

FIG. I is a side elevational view, in longitudinal cross section, of acapacitor embodying the invention;

FIG. 2 is a partial view of the rotor member of the capacitorillustrated in FIG. 1, also shown in longitudinal cross section, andillustrating mechanical details of the antibacklash screw thread portionthereof;

FIG. 3 is a vertical cross-sectional view taken along the line 3-3 ofFIG. 2 in the direction of the arrows; and

FIG. 4 is an outer end view of the rotor member as seen from the planeindicated at 4-4 of FIG. 2.

Referring now in details to the drawings, the capacitor comprises astator unit designated, generally, as 10 and a rotor unit 11. The rotorunit is threadedly mounted in a rotor bushing member designated,generally, as 12.

The stator unit 10 comprises a metal disc-shaped body portion 14 havingan external, integrally formed axial extension 15. The free end of theextension 15 is headed, as indicated at 16, for retaining a conductor(not shown) prior to and during the formation of a soldered connectionwith the conductor. The conductor, or other circuit element connected tothe extension 15, provides a utilization connection for energizing thestator unit 10.

The stator unit 10 has an inner annular groove 18 formed therein and anouter annular groove 19, the two grooves 18 and 19 being of rectangularcross section and precisely concentric-with the common longitudinal axisof the stator unit I0 and the rotor bushing 12. Four stator tubes, 21,22, 23 and 24 are precision fitted in the grooves 18 and I9 and are ofequal lengths. The stator tubes 21-24 are permanently secured by thesoldering. The stator tubes 21-24 are formed of invar or a similar alloywhen a low-temperature coefficient of capacitance is desired. Where verylow loss is important, the electrode tubes are made of silver or othermaterial of low specific resistivity. An integrally formed cylindricalshank 26 extends from the body portion 14 of stator threaded sections320 and 32b for the purpose hereinafter more particularly described.

The rotor unit 11 also comprises four rotor tubes 34, 35, 36, 37 ofequal lengths formed of metal, as are the stator tubes 24, 25 describedabove. Inward movement of the rotor unit 11 is limited by a stop member38 of insulating material suitably retained within the innermost rotortube 37 and which abuts the shank 26 in the position of maximumcapacitance. The innermost tube 34 is press fitted or otherwisepermanently and accurately secured in place, being fitted against thelateral wall of a cylindrical recess 39 formed in the inner end of therotor body 31. The intermediate tubes 35, 36 are similarly fittedagainst the inner and outer walls, respectively, of an annular groove 40formed in the end of the rotor body 31, the depth of the groove 40 beingthe same as that of the recess 39. The outermost tube 37 is similarlyfitted against a cylindrical outer end surface of the rotor body 31. Forlower values of maximum capacitance, the member of rotor tubes may bereduced to a lesser number, or to a single tube for minimum capacitance.

Each of the four rotor tubes 34 through 37 extends to an adjustableextent within and overlies one of the four stator tubes 21 through 24with substantially uniform radial spacing, the external surface of thestator shank 26 operating as an innermost stator electrode cooperatingwith the innermost stator tube 34.

Means is provided for rotatively and axially adjusting the rotor unit 11within the rotor bushes 12 for tuning or capacitance adjustment. To thisend, the outer end of the metal body portion 31 of the rotor unit 11 ispressed into substantially square shape, as indicated at 43 in FIG. 4,as by a swedging operation, and provided with a comparatively large,substantially concentric square opening or slot 43a for the reception ofa unit coaxially within the innermost stator tube 21.

The stator unit 10 is rigidly connected to the rotor bushing 12 by ahollow cylindrical housing or sleeve 27 formed of a glazed ceramicmaterial such as alumina. Glass is also suitable. At its ends, theexternal surface of the housing 27 is metallized to provide two thincircumferential bands 28 of metal intimately and positively adhered tothe surface of the sleeve. In the drawings, the thickness of themetallized bands 28 has been exaggerated for clarity of illustration.The metallized bands 28 are connected to the periphery of the statorunit 10 and to the periphery of the rotor bushing 12 by rings of highmelting point solder 30. During the soldering operation, the parts areso positioned that the longitudinal axes of the stator unit 10 and therotor bushing 12 are precisely aligned.

The rotor unit 11 comprises a metal body portion 31 having two axiallyspaced series or groups of external helical threads 32a and 32b inthreaded engagement with complementary internal thread 33 formed in therotor bushing 12. The threads 32a and 32b constitute two axially spaced,threaded sections or groups of threads which are separated by a thin,tubular, nonthreaded section 320 of substantially reduced diameter. As asalient feature of this invention, diametrically opposed portions of thenonthreaded section 32c are cut away to provide an opposed pair ofelongated openings 32d, 32e. The openings 32d, 32e in the nonthreadedsection serve to reduce the compressional strength of said nonthreadedsection, especially in small diameter rotary units, to more readilypermit axial deformation thereof for the purpose hereinafter appearing.It is also to be noted that the nonthreaded section is deformed toprovide opposed, outwardly bulging portions, as indicated at 32f and32g. Such deformation of the rotor unit 11 results in relative axialdisplacement of the rodlike tool of square cross section to permitmanual adjustment in the manner of a screwdriver. The provision of thecomparatively large squareshaped tool slot permits the use of anadjustment tool, extruded, for example, of a tough synthetic plasticinsulating material, instead of the usual metal screwdriver heretoforeused. The use of a nonmetallic insulating material for the tuning oradjustment tool is of particular importance in high frequencyapplications where the proximity of metallic masses to the capacitorplates or tubes would effect a change in the absolute capacitance beingtuned to. The use of a square tool opening moreover provides for thegreatest torque strength in tuning with the simplest fabrication. Thesquare slot also eliminates scraping of the internal threads of therotor bushing, as was commonplace in rotors heretofore devised whereinscrewdriver slots were provided for use with screwdrivers as the tuningtool.

The capacitor is shown provided with an end closure cap 47 threadedlyengaging external threads 48 formed on the rotor bushing 12. An airtightseal is provided by a sealing disc 49 formed of resilient material. Aretaining strap 51 formed of flexible material interconnects the cap 47and the rotor bushing 12, so that the cap 47 will not become misplacedduring its removal for capacitance adjustment.

Referring to FIG. 2 it is to be noted that the non threaded section 32cof the rotor unit 11 will initially be of cylindrical shape. By means ofa suitable spinning or forming operation, the thin-walled portion 320 iscaused to assume the outwardly convex bulges 32f, 323 The formation ofthe opposed bulges 32f, 32g brings the two series of threaded sections32a and 32b axially closer together than they were at the time of theircutting as a single continuous thread. The threads 32a and 32b are thusresiliently helically misaligned. When threaded into the bushing 12, thethread sections 32a and 32b are thus axially forcibly urged apart by theinternal threads 33 of the bushing 12 toward their initial spacingbefore the formation of said bulges. The bulges 32f, 32g are resilientldeformable, to a certain extent, toward the initial cylindricaconfiguration. Ac-

cordingly, the axially spaced threaded sections 320 and 3211 areyieldingly urged toward each other by the bulges 32f and 32g and theresulting frictional force efi'ectively locks the rotor body 31 in anydesired position in the bushing 12 to which it is adjusted by means of atool of square cross-sectional shape inserted in the square recess 340as hereinabove described,

While I have illustrated and described herein only one form in which myinvention can conveniently be embodied in practice, it is to beunderstood that this form is given by way of example only and not in alimiting sense. The invention, in brief, comprises all the embodimentsand modifications coming within the scope and spirit of the followingclaims.

What I claim as new and desire to secure by Letters Patent is:

1. An adjustable capacitor comprising a rotor portion and a statorportion, relative axial displacement between said stator portion causinga variation in the capacitance of said capacitor; an interiorly threadedmember mechanically connected to one of said capacitor portions and anexteriorly threaded member mechanically connected to the other capacitorportion, the threads of said interiorly threaded member being incooperating engagement with the threads of said exteriorly threadedmember for defining the axis of said axial displacement, said exteriorlythreaded member having an axial bore and an annular groove formedtherein, said groove defining, with said bore, a thin-walled portion ofsaid exteriorly threaded member located intermediate two separateaxially spaced threaded portions thereof, said thin-walled portioncomprising a pair of diametrically opposed, resiliently deformable,outwardly bulging portions which yieldingly heli cally misalign saidseparate threaded portion when free from engagement with any cooperatingthreads, said threads being forcibly aligned by the threads of saidinteriorly threaded member when in engagement therewith to produce acontinuous frictional engagement between said threaded members forresisting relative rotation therebetween, said bulging portion beinginterspaced by elongated through openings formed in said thin-walledportion.

2. An adjustable capacitor as defined in claim 1, wherein said bulgingportions are of convex, radially outwardly extending configuration.

3, An adjustable capacitor as defined in claim 1, having an elongatedexteriorly threaded adjustment screw having a uniform pitch throughoutthe threaded portion thereof, said screw having an axial bore and atleast one annular groove formed therein which extends inwardly towardsaid bore, the threads of said screw being interrupted by said groove,said bore and said groove defining a thin-walled portion of said screwlocated intermediate axially spaced threaded portions thereof, saidthin-walled portion comprising a pair of diametrically opposed,resiliently deformable, outwardly bulging portions which, with thethreads of said screw free from any co operating threads, maintain saidaxially spaced portions of said screw threads, said spaced portions ofsaid thread screw becoming yieldingly aligned by axial elongation ofsaid screw accompanying simultaneous engagement of said spaced portionsof said screw threads with cooperating internal threads, said elongationproducing spring-pressed frictional engagement between said spacedportions of said screw threads and said cooperating threads.

4. An adjustable capacitor as defined in claim 3, wherein said bulgingportions are of convex, radially outwardly extending configuration.

5. An adjustable capacitor as defined in claim 4, including a squarerecess formed in the outer end of said adjustment screw forinterengagement with a manually operated adjustment tool.

1. An adjustable capacitor comprising a rotor portion and a statorportion, relative axial displacement between said stator portion causinga variation in the capacitance of said capacitor; an interiorly threadedmember mechanically connected to one of said capacitor portions and anexteriorly threaded member mechanically connected to the other capacitorportion, the threads of said interiorly threaded member being incooperating engagement with the threads of said exteriorly threadedmember for defining the axis of said axial displacement, said exteriorlythreaded member having an axial bore and an annular groove formedtherein, said groove defining, with said bore, a thin-walled portion ofsaid exteriorly threaded member located intermediate two separateaxially spaced threaded portions thereof, said thinwalled portioncomprising a pair of diametrically opposed, resiliently deformable,outwardly bulging portions which yieldingly helically misalign saidseparate threaded portion when free from engagement with any cooperatingthreads, said tHreads being forcibly aligned by the threads of saidinteriorly threaded member when in engagement therewith to produce acontinuous frictional engagement between said threaded members forresisting relative rotation therebetween, said bulging portion beinginterspaced by elongated through openings formed in said thinwalledportion.
 2. An adjustable capacitor as defined in claim 1, wherein saidbulging portions are of convex, radially outwardly extendingconfiguration.
 3. An adjustable capacitor as defined in claim 1, havingan elongated exteriorly threaded adjustment screw having a uniform pitchthroughout the threaded portion thereof, said screw having an axial boreand at least one annular groove formed therein which extends inwardlytoward said bore, the threads of said screw being interrupted by saidgroove, said bore and said groove defining a thin-walled portion of saidscrew located intermediate axially spaced threaded portions thereof,said thin-walled portion comprising a pair of diametrically opposed,resiliently deformable, outwardly bulging portions which, with thethreads of said screw free from any co operating threads, maintain saidaxially spaced portions of said screw threads, said spaced portions ofsaid thread screw becoming yieldingly aligned by axial elongation ofsaid screw accompanying simultaneous engagement of said spaced portionsof said screw threads with cooperating internal threads, said elongationproducing spring-pressed frictional engagement between said spacedportions of said screw threads and said cooperating threads.
 4. Anadjustable capacitor as defined in claim 3, wherein said bulgingportions are of convex, radially outwardly extending configuration. 5.An adjustable capacitor as defined in claim 4, including a square recessformed in the outer end of said adjustment screw for interengagementwith a manually operated adjustment tool.